Warped substrates are a problem which prevent the substrates from being chucked fully on a process chamber pedestal. Such warpage leads to a delay in or ceasing of the substrate processing.
For example, epoxy mold compounds are used to encapsulate dies in substrate packaging. These compounds bow and warp after thermal processes due to inhomogeneous heating and cooling, causing non-uniform expansion/contraction rates in current process equipment. Conventional thermal processes utilize directional heat transfer via radiative, convective or conductive thermal processes. The directionality results in anisotropic expansion and contraction rates. When operated near the thermoplastic regime, non-uniform cooling and, subsequently, contraction rates give rise to a warped substrate. Such warp and bow effects are frequently observed and imply that the substrate is being processed close to the thermoplastic regime of the substrate, giving rise to substrate warpage beyond acceptable levels.
Being able to detect and measure the warpage before, during or after any process would result in benefits to production throughput and yield.